I've posted here before asking about kinks and sexual connection in old vs new poly relationships. Here is the ongoing dilemma which I guess sparked the question, and now it's coming to a head:

When I first met my SO we had a crazy connection. Like physically the most intense I've ever had. We'd have sex 5 times a day, never sleep, do very extreme BDSM, explore each other's fantasies.... etc. It was amazing, I've never felt so wanted or so turned on, I felt he really knew my body and I knew his, it was so special.

After a while, I noticed that not only things calmed down in a way you'd expect when a relationship gets established, but also the kink levels dropped, a lot. A few major changes I noticed:

He has delayed ejaculation but used to come in me once every week or two. Then once a month and with decreasing regularity - now we're down to maybe every 6 months, and it takes me pointing out how long it's been and him making an effort not to come for a few days. So it no longer happens naturally.

He is no longer interested in outdoor sex, SM, DS, degradation, anal or any of the other things that turned us both on so much... well with me at least! It happens if I ask a few times but it's never the same, and feels he's doing it to make me happy so it's really lacking intensity. He will stop as soon as I've come, there isn't even a question of him coming this way because I don't think he's turned on enough by doing it.

There are no more filthy text, replies to mine are like "that sounds good" and... idk. I just don't feel even a quarter as exciting to him any more.

Sex positions - he only seems to want to have sex now doggy style, it's always been his favourite position but we used to have lots of variety and him on top is my favourite. But he responds badly to me asking for it and gets defensive and says he doesn't really enjoys it (even though it used to turn him on a lot).

Now you can probably gather I analyse a lot, it's in my nature, and he says he feels under scrutiny and he knows that underneath his "super lover" thing he does with new partners he is actually insecure and overly sensitive to feeling like his performance is criticised. So apparently it was enough that I once responded unenthusiastically to a flirty text about anal that now we just don't have it any more, or that I once declined sex as soon as we got in that he stopped bending me over and taking me when he likes. He says I have a controlling nature and I know he has a point, but this is something I'm working on and I think I've made great progress with. But trying to tease out what is going on with how vanilla our sex life has become makes him defensive. Trying to talk about treatments for delayed ejaculation (which has apparently caused him problems in EVERY relationship he's been with, and there are effective treatments online) makes him super defensive. Trying too hard to flirt about the things I crave makes him defensive. And when he gets defensive I get emotional. I'm walking around with a craving for the sex we used to have and the things he wanted to do to me when now he wants to snuggle. I know intensity dies over time but surely the ability to be playful and dirty doesn't have to?? I grieve for the connection he used to have towards me, and this is compounded by the fact that I still want him just as badly as I did at day one. None of this is being helped by the fact that in my last relationship I was constantly rejected sexually by a lower-libido partner and that in his last relationship he retaliated against his ex-wife's lying to him by refusing to have sex with her for a year. So we have a complex connection to our sexualities...

But here is where things are getting even more complicated: he has a new poly partner who sounds great (I'm supposed to meet her soon) and I've just found out - yes I asked, and in a way I'm glad I did - that they do kink, anal, SM. I've been getting these needs met with another lover but have always wanted them in my primary relationship. Finding out that he has (at least for now) lost the ability to express himself sexually this way with me but can with her is saddening. His argument is "we've been together for over 2 years, we have sex nearly every time we see each other so what's the problem" and when I tried to say I am happy he's found someone to explore those things with but it is difficult for me when I've been craving and asking if we can do these things for ages... well then he said I make him feel bad. Idk. I guess my questions are -

Am I being neurotic or is there a problem here?

Can it be fixed or should I just decide if I can deal with my primary relationship being vanilla and my partner only being able to fully express his sexuality outside the relationship (I can't) and also feeling I'm to blame for all of it?

Any insights really... I feel a bit lost. I cannot go on feelings this way and we can't go on having arguments about it. We are giving each other mental blocks and insecurities and I feel we're in a loop. There's no way he'd agree to have any form of therapy... He wants me to "just chill" and believes that if we are actually able to go for a few months without talking about any of these issues things will resolve themselves. I don't know if I can - or shall I just grow up and force myself to? When I do I end up being sulky or sad but maybe I can try harder.